HTML code of the example :
        
<HTML>
<select id="ex3-day">
<option value="01">01</option>
...
</select>
<select id="ex3-month">
<option value="01">01</option>
...
</select>
<input type="text" maxlength="4" readonly="true" id="ex3-year" size="4" />
<input type="button" id="example-3-bt"/>
</HTML>

We use the custom event `onSelectEvent` to catch the value of the
selected date and update the value of the combo-boxes and textfield.

<script type="text/javascript">
var customSelect = function(o) {
    $('ex3-day').value = o.date.format('d');
    $('ex3-month').value = o.date.format('m');
    $('ex3-year').value = o.date.format('Y');
};
new Calendar('example-3', {
    source: 'example-3-bt',
    events: {
        onSelectEvent: customSelect
    }
});
</script>
        
<select id="ex3-day">
    <option value="01">01</option>
    <option value="02">02</option>
    <option value="03">03</option>
    <option value="04">04</option>
    <option value="05">05</option>

    <option value="06">06</option>
    <option value="07">07</option>
    <option value="08">08</option>
    <option value="09">09</option>
    <option value="10">10</option>
    <option value="11">11</option>

    <option value="12">12</option>
    <option value="13">13</option>
    <option value="14">14</option>
    <option value="15">15</option>
    <option value="16">16</option>
    <option value="17">17</option>

    <option value="18">18</option>
    <option value="19">19</option>
    <option value="20">20</option>
    <option value="21">21</option>
    <option value="22">22</option>
    <option value="23">23</option>

    <option value="24">24</option>
    <option value="25">25</option>
    <option value="26">26</option>
    <option value="27">27</option>
    <option value="28">28</option>
    <option value="29">29</option>

    <option value="30">30</option>
    <option value="31">31</option>
</select>
<select id="ex3-month">
    <option value="01">01</option>
    <option value="02">02</option>
    <option value="03">03</option>

    <option value="04">04</option>
    <option value="05">05</option>
    <option value="06">06</option>
    <option value="07">07</option>
    <option value="08">08</option>
    <option value="09">09</option>

    <option value="10">10</option>
    <option value="11">11</option>
    <option value="12">12</option>
</select>
<input type="text" maxlength="4" readonly="true" id="ex3-year" size="4"/>
<input type="button" id="example-3-bt"/>